Patients with gastrointestinal carcinomas are studied for evidence of reactivity against tumor-associated determinants expressed on both fresh and cultured syngeneic or allogeneic tumor cells using immunofluorescence and immunoperoxidase staining techniques. Various human malignant cell lines have been established in vitro and are being characterized morphologically and immunologically. An experimental model of pancreatic carcinoma has been developed in hamsters. Tumor-associated antigens have been isolated from both animal and human pancreatic cancers and are being investigated for possible applications to immunotherapy or methods of immunodiagnosis. Tissue-specific antigens have been isolated and are being investigated for possible use in immunotherapy of pancreated carcinoma. Monoclonal antibodies have been developed to tumor-associated determinants in both hamster and human pancreatic cancers. Monoclonal antibodies have been demonstrated to be cytotoxic to pancreatic cancer cells both in vitro and in vivo. Conjugation of radionuclides to monoclonal antibodies has resulted in cell-kill both in vitro and in vivo as well as permitting imaging of tumor sites in tumor-bearing experimental animals. Tolerance of various normal and surgically-manipulated tissues to intraoperative radiotherapy is being investigated in dogs to determine both acute and long-term toxicity.